1. Field of the Invention
The invention relates to the field of car door construction. More in particular, the invention relates to systems for tuning and damping acoustic vibrations in car doors.
2. Description of the Related Art
Car customers are attracted to quality car build. One of the universal tests they use to determine quality is to listen to the sound a car door makes when it is closed. If the sound reverberates, or is "tinny", or sounds like a drum, the quality of the car is perceived as poor. However, if the sound is "solid", e.g., it lacks reverberation, the quality of the car is deemed high. Thus, the sound a car door makes when it is closed is often important in making a sale.
The problem of low quality sounding car doors arises from the fact that car doors are hollow. The typical car door below the window opening has an outer skin and an inner panel. There is a significant space between the two in which are located such things as structure for raising and lowering the window glass, and for door latching. Typically, such internal structure is attached to the inner panel or the rear latch area of the door. The outer skin typically does not have anything mechanically attached to it so the outer appearance of the door will appear uninterrupted. Accordingly, the outer skin acts like a drum skin and vibrates unwanted acoustic waves along the length and width of the door, as well as across the internal space.
Car doors are now required to have a side impact structure installed in the interior of the door which extends along the length of the door. The purpose of the impact structure is to absorb crash impact from the side and protect passengers seated adjacent to the doors. These structures are usually beams but have had little effect, if any, in damping unwanted acoustic vibrations in the doors.
Side impact beams can take various shapes. U.S. Pat. No. 5,080,427 to Sturrus et al. discloses a roll-formed impact beam which can be attached to the outer skin or inner panel by fasteners or adhesives.
Another, more substantial side impact structure is shown in U.S. Pat. No. 4,969,680 to Shimoda. Here the side impact structure is a panel consisting of two corrugated plates attached to each other with the ridges and grooves of the respective corrugations confronting each other. The panel extends the horizontal length of the door. Vertically, the panel extends from the outer skin in an upper region near the window opening to the inner panel at the bottom where it is spot welded in place. The use of brackets is not disclosed. Shimoda discloses that the panel may double as the outer skin or may be covered by a decorative outer skin with some clearance therebetween. There is no discussion concerning damping acoustic vibrations.
A beam held in place by brackets on the inner panel is shown in U.S. Pat. No. 5,404,690 to Hanf. A beam is disclosed which extends the horizontal length of the door. The beam is crimped on the ends to provide a mounting area for end brackets to connect the beam ends to the inner panel. A center bracket mounted on the inner panel fixes the beam at its mid-section. There is no disclosure by Hanf of utilizing the beam or its brackets to dampen the acoustic vibration of the outer skin.
Accordingly, there is a need in the art for systems to truncate and dampen sound waves traveling through the outer skin of a door so as to provide a high quality closing sound.